Maintaining clean git history is encouraged, but not enforced.
We use rebase workflow, it's OK to rewrite history during PR review process.
-Avoid @mentioning people in commit messages and pull request descriptions, as such messages create a lot of duplicate notification traffic during rebases.
+Avoid @mentioning people in commit messages and pull request descriptions (they are added to commit message by bors), as such messages create a lot of duplicate notification traffic during rebases.
# Architecture Invariants